Injection molding has long been one of the methods of choice for the fabrication of multiple similar parts in polymers. However, when the parts to be molded require, e.g. high precision dimensions within detailed structures, the preparation of a suitable mold rapidly becomes difficult. With some simple part geometries it may be possible to directly machine mold surfaces. However, in more complex situations it is known to prepare surfaces of hard copper by such techniques as diamond turning, direct cutting, and broaching, and then using the copper master to produce electroforms in nickel for subsequent polymer molding processes.
The use of such electroforms is a useful technique, but limited by the lack of ways to install these surfaces into molds. For example, electroformed stampers have been mounted to a thick plate by mechanical fasteners, by perimeter welding, by soldering, and by brazing. Monolithic platings, e.g. 12.7 mm (0.5 inch), have been fabricated for direct insertion into molds. However none of these are generally viable techniques having broad commercial application.
A notable exception is the compact disc industry; masters are often made using photolithography, and electroformed stampers produced off these masters. The subsequent operations of transforming them into a circular part with a hole in the center allows for installation into the mold by using two rings, an inner and outer retaining ring, which captures or ‘picture frames’ the periphery of the electroforms as well as forming the two diameters of the product. For products larger than 130 mm, however, this technique is not practical because such retention at the outside diameter and the inside diameter is not sufficient to constrain deflection of the stamper during the process. The art is still in need of a method to provide a mold having an insert with a precision surface that is effective and yet applicable to a wide range of part sizes and geometries.